This invention relates to optical integrated semiconductor circuits.
Despite intensive efforts in recent years in the fields of optical communications and integrated optics, very few examples of monolithic integration of semiconductor optical devices have been achieved thus far; usually the laser cavity is formed by a pair of parallel cleaved facets, so that the laser source becomes a discrete device incapable of monolithic integration with other circuit components. To overcome this restriction much attention has been devoted to the use of gratings to produce the optical feedback required for integrated devices, [e.g., F. K. Reinhart et al., Applied Physics Letters, Vol. 27, p 45 (1975)], but attempts to couple light from an optical cavity defined by these gratings into a low-loss passive waveguide have been accomplished with low efficiencies, typically less than one percent [see also, K. Aiki et al., Appl. Phys. Let. Vol. 29, p. 506 (1976)]. An alternative approach to the fabrication of integrated lasers utilizes vertical mirrors made by etching or sputtering. C. E. Hurwitz et al., Appl. Phys. Let., Vol. 27, p. 241 (1975), coupled light from an etched Fabry-Perot cavity laterally into a thick (12 .mu.m) waveguide with a differential quantum efficiency of about 3.5%. Y. Suematsu et al., IEEE J. Quant. Electr., Vol. QE-11, p. 457 (1975), utilized phase coupling to transfer light from etched or sputtered resonators into a passive waveguide, but data on efficiencies are not given in that work.